What does this mean? (Usps shipping)

I shipped a package out from mercari and it was supposed to be delivered on the 21st but then I got a notification saying it's a day delayed and now it's saying it's being held at the post office at customers request but I didn't request that and neither did the buyer. So I'm confused as to why my package is being delayed for so long? It's already been scanned through the shipping process and is sitting at the post office near my customers address, Here's my tracking info if any of you could help me out lol